The primary goals outlined in this trial were to carefully characterize subjects who have a well defined nucleoside exposure history with respect to their symptomatic state, their CD4 count trajectory, and their virologic profile, and to relate this to the response to new antiretroviral interventions in HIV infected patients who had been treated either with monotherapy (ADV of ddl ) or dual combination therapy (ADV/ddl or ZDV/ddC) while participating in ACTG 175. Results of this trial are not yet available.